Today was my first time visiting Grundlsee, and it was definitely worth it.
I was fortunate enough to choose a beach and it turned out to be the right decision.
The parking fee is €8 for the entire day, which I think is reasonable. There is no entrance fee for the Strandbad to be paid. However, the lido is more of a sunbathing area with a small jetty for jumping in and it's also perfect for stand up paddleboarding.
Toilets are available in the parking lot, but there is no food and drink service.
The lake is truly stunning and ideal for stand up paddleboarding, in my opinion. There are already a few boats out on the water, but everything is well spread out on this vast lake.
It's definitely worth a visit!